Speed sensor : wrong auto-calculation
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Speed sensor : wrong auto-calculation
When using auto-calculation with a speed sensor, wheel circumference is over estimated on Karoo 2.
I tried the following test: connected the same speed sensor to both my Garmin Fenix and my Karoo 2.
Both are configured with auto-calculation of wheel circumference. My wheel is 700x35c, announced circumference is 2168mm, measured by myself: 2197mm.
After my ride, estimated circumference was:
Garmin Fenix : 2183mm, almost what I measured.
Karoo 2 : 2249mm, way to high.
Here are the stats of my ride, started and stopped at the same time on both devices :
Garmin Fenix: 31,87km, 1:22:20, 23,2km/h
Karoo 2 : 33,27km, 1:22:52, 24,2km/h
How is such a difference possible, how does the Karoo 2 evaluates the wheel circumference ?
Thanks for your help,
Luc
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Official comment
Hi All,
This issue has been addressed in today's release. Thank you for bringing this to our notice!
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@Arne I do the same thing and I'm continually disappointed to see no fix.
I was listening to a recent episode of the Marginal Gains podcast. They were talking about their first bike computers and lamenting on how the actually had to manually set their wheel size in the computer. It made me a bit sad that we still have to do this with our $400 Karoo2.
I ended up measuring my wheel circumference. It was very enlightening on why accurate auto calibration is important. I'm running a 700x25 tire (Continental GP5000). The chart says the standard is 2105mm. My measurements at 90psi:
- Without rider weight: 2121mm
- With rider weight (170 lbs): 2091mm
This little exercise showed that that tire brand/model can impact circumference. More importantly, bike/rider weight can have a large impact. While I didn't test, I'm assuming tire pressure would also affect tire circumference. In other words, if I gain/lose weight (or add/subtract to the bike) or adjust PSI my circumference could change enough to through off my accuracy. It's a lot to ask to remeasure circumference on each ride.
While I appreciate the continued development and new features, this needs to be fixed ASAP. Accurate data is the cost of entry in this category. It's the one thing that makes me hesitant in recommending the K2 to other riders.
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Hammerhead is pushing updates regularly that usually include a number of bugfixes, which is great to see. However, I personally don't understand how this issue does not get a bigger priority, as to me it seems more crucial than some of the other bugs that get fixed. Speed sensors are basically unusable right now as long as you don't want to go through the hassle of manual calibration, which actually I won't do as I just fall back to GPS and I think something basic like this should just work. Using GPS is an okay fallback, but as we know, it's speed readings are delayed and it doesn't work great in areas where GPS reception is compromised.
It would be great to get another status update from the team on this, is there a way to escalate an issue?
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Just chiming in here that I have the same problem with Auto calibration. I added the Wahoo Speed sensor last week and already noticed average speeds being unusually high. Today I did a route I usually do which was 67km but it ended up being 71km on the Karoo2 which is a 6% difference. After correcting the distance on strava based on GPS it shows 67km again. Also average speed went down by 3kph (as well as estimated watts and calories) which is a lot. Would highly appreciate a proper fix on this as right now the auto calibration is pretty useless.
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There’s definitely a problem with auto calculation. On a typical 35 mile ride my K2 is a bit more than a mile higher than all the other Garmin and Wahoos in the rest of my cycling group.There’s definitely a problem with auto calculation, And consequently it inaccurately shows a higher average speed. I’ll be trying manual calculation to see if I come in closer to the the truth.
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Any updates here?
I have my Karoo 2 connected to a Garmin Speed 2, and on my last ride had a distance that was 3.4% higher than two riding buddies on the identical route. Both of them are using Garmin Edge 530 computers, one with an identical speed sensor to me (Garmin Speed 2) and one using GPS. Their deviation was under 0.4% against each other.
It looks like this has been a very slow bug to fix, and I'm hopeful that it's updated soon. I know that others here are suggesting measuring roll-out manually, which I will do, but I adjust my tire pressure based on conditions (gravel vs road, wet vs dry) and don't want to be doing that all the time when cheaper bike computers from Garmin are flawless in their calibration.
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Hi all, we are monitoring this post for all the inconsistency reports and it is true that 7% error is just unacceptable. I am trying to collect more information so any help would be greatly appreciated. We have not seen all the riders and only a small minority group of riders, and we need to isolate the case and identify any pattern.
Could you please fill this form Auto-wheel circumference inaccuracies?
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I would request everyone to please provide us with the details on the form here
https://docs.google.com/forms/d/e/1FAIpQLSfWU6OJBl68-5ush6netTcnWIetVvqJXdxTV2I5L7nGCVxs2w/viewform
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@Vito HH support already wrote:
https://support.hammerhead.io/hc/en-us/community/posts/1260800782169/comments/1260802818730
https://support.hammerhead.io/hc/en-us/community/posts/1260800782169/comments/1260802978249
Here are the steps to manually set the wheel circumference on your Karoo: https://support.hammerhead.io/hc/en-us/articles/360048580233-Setting-the-Wheel-Circumference
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Just a thought... I wonder if the unit drops the connection with the sensor every now and then? It would then have to increase the distance travelled per revolution to make up the lost distance from the sensor.
Does it work better with sensors fitted to the front wheel? They're closer to the unit with less things to interfere with the signal or does the unit itself have difficulty keeping up with the data, possibly from multiple sources/sensors? Or, is it just a calculation error? How about the environment? Could there be interferrence and/or reflections that would 'confuse' the signal (ie urban environments)?
When does the auto calibration take place? At the very begining of a ride, possibly when you're starting off and out of the saddle (weight transfers and bike angle could affect the rolling circumference-the more leant over you are the smaller the circumference).
I suppose it has to happen immediately to get a reading up to the display. Why not make further calibrations as the rider settles?
I've heard that braking can affect the measurements as well (changes rolling resistance), so if it auto calibrates as you're starting off downhill (or in stop/go heavy traffic or even tight, twisty urban areas), measurement could be affected.
How about doing the auto calibration a number of times per ride? It could use the gps to identify a flat section and look for a constant, steady speed before doing the auto calibration. Or, just continually update versus gps, it would only get more accurate like this. Or... just use the speed sensor to smooth out the gps speed reading and not use it for the final distance/speed measurements.
How do the others (Garmin etc) do their auto calibration?
Just thinking alloud really and have not seen any of these suggested. Sorry if they're silly suggestions/thoughts but thought I'd add them, you never know! -
The latest software lists a fix for the wheel circumference calculation algorithm. Can anyone from Karoo confirm if that is supposed to address this issue that has been around for many months now? I guess I'll have to give it a shot on my next ride but it would be nice to know if it is targeting this specific issue or something different.
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FYI, I just did a ride this morning after installing the latest Karoo2 software update with auto-calculation turned back on for my Wahoo speed sensor. When I compare the distance from the speed sensor to the GPS distance, they are only .02 miles different for a 23 mile ride. This is MUCH closer than I was seeing before with the auto calibrated circumference so "hopefully" this has been fixed once and for all. I'll be interested to hear of others have similar success with the latest software update.
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I also noticed this problem. I think there is something wrong with the Auto Wheel Circumference. This is why my distance data did not match or even come close to matching my friend's distance data when comparing on Strava. Strava takes the Garmin speed sensors' data over the GPS data and uses this to compute the distance traveled. This is also why on the Karoo dashboard, the distance matches my friends distance- the dashboard uses the GPS data.
Auto wheel circumference works fine for my Garmin 530 edge, but the Karoo 2 overestimates my wheel's circumference and therefore, overestimates my total distance traveled. You have to "revert distance" on Strava to correct it so it uses the GPS data instead. Or, you can manually enter your wheel circumference. I am going to manually enter the wheel circumference my Garmin auto calculated into the K2.
I think that Hammerhead needs to look at the Auto Wheel Circumference and how it is computed. It is off and nowhere near accurate. Garmin calculated my wheel at 2127mm and Karoo 2 calculated 2203mm. Most online charts put my wheel at 2136mm. Over a 29.3 mile ride this added about 1.2 miles to my total distance. The GPS was accurate in calculating the distance...
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Hi Abhishek,
Thanks for your answer.
I have done more tests with another bike, another wheel size, another sensor and another device (Garmin Edge).
I did 3 times the same process:
Unpair the sensor from both Karoo 2 and Garmin Edge, re-pair the sensor to both devices in configuration 'auto-calculation', take a ride for about 6km, then check the calculated circumference on the devices.
Here are the results of the 3 measures:
Garmin Edge: 2236mm - 2238mm - 2247mm
Karoo 2: 2423mm - 2406mm - 2412mmAccording to Strava, Garmin is closer to reality than Karoo 2: GPS measured distances are correct for both device as Strava corrected ("reversed") distances are approximately the same for both devices and correspond to what the Garmin Edge measures. Also, during the ride, if I change the precedence on the Karoo 2 and put the GPS on top, I have the correct instant speed.
I agree there is a percentage of error, but the result here is a difference of 1-2km/h on average speed for the ride.
I know I can enter circumference manually (for me it would mean copy the value measured by Garmin to Karoo 2), but I would like to get rid of my Garmin Edge that has other problems. I'm still disappointed by the difference of measure for a device that wants to be the "World's finest cycling computer".
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I have been posting about this issue as well. At first, I thought it might a battery issue with the Garmin speed sensor. I replaced the battery with a brand new battery and again, it overestimated the wheel circumference and therefore the total distance of the ride. It is disappointing to say the least that the K2 can't auto calculate a wheel circumference.
I think someone needs to look at this problem...
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Ditto. I ride with my wife and my Garmin was always close but slightly behind hers. Switched to the Karoo 2 and noticed a jump in speed and distance when riding regular routes. I’m now 5% above her, 1 mile for every 20 we ride. Performed a distance correction in Strava and all my rides on the Karoo 2 were reduced by about 5%. Definitely an issue with the Karoo 2 auto-calculate.
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